Field Of The Invention
This invention relates to a ecologically improved, essentially solvent free process for the production of a chip resistant finishes on an optionally primed substrate by application and stoving of an aqueous based chip resistant coating composition, an aqueous based filler, an aqueous based finishing paint and, optionally, a clear lacquer. The process according to the invention enables the production chip resistant finishes particularly in the automotive field.
The production of chip resistant intermediate coatings has long been of considerable interest, particularly in the automotive field. Hitherto, chip resistant coatings have been produced on the basis of solvent-containing primers. Thus, DE-OS 33 37 394 corresponding to U.S. Pat. No. 4,606,947 describes a chip resistant protective paint based on polyesters with blocked isocyanates which contains standard paint solvents.
Although it is known that water-dilutable coatings, such as primers and fillers, can be produced, no water-dilutable coating composition suitable for the production of so called non-chip or chip resistant intermediate films has hitherto been produced. Thus, it is standard practice for example to produce water-dilutable primers from water-dilutable resins, such as polyesters, polyacrylates, and/or corresponding dispersions and/or emulsions containing suitable crosslinking agents, preferably water-dilutable aminoplastics. Aqueous dispersions or emulsions based on polyesters, polyethers and polyacrylates and crosslinking agents containing masked reactive isocyanate groups are described, for example, in DE-A-35 45 618 and in EP-A-0 140 323. Dispersions such as these are used, for example, as base paints for two-layer coatings. Binder systems based on epoxy dispersions containing water-dispersible, blocked isocyanates are also basically known (GB-A 2,127,829).
In recent years, solvent-containing systems have been vigorously criticized because of the ecological problems they cause on account of their solvent content. However, the aqueous systems hitherto used are also attended by serious disadvantages. Thus, it is known that one of the main difficulties in the formulation of aqueous, isocyanate-containing paint systems lies in their inadequate shelf life. Conventional water-dilutable stoving filler systems generally have mechanical disadvantages compared with solvent-containing systems in regard to chip resistance and elasticity and, accordingly, were not used for so called non-chip coatings. Lacquer systems based on aqueous polyurethane dispersions also have the disadvantage of rapid film formation which makes them unsuitable for application by electrostatic film forming systems, such as for example high-rotation bells. Tools are in danger of solvent contamination. Neither are the known aqueous primer systems suitable for wet-in-wet application with the known solvent-containing chip resistant intermediate coatings, because losses of surface quality are inevitable.
In view of the increasing demand for modern, i.e. ecologically safe, paint systems and the increasing legislative pressure for a reduction in the emission of organic volatile constituents in paint systems, for example automotive assembly-line paint systems, there is a continuing need for water-dilutable lacquer systems. In the field of chip resistant primers, this has given rise to the problem of providing an aqueous binder system which satisfies the high quality requirements of known solvent-containing binder systems, but does not have any of the disadvantages of hitherto known aqueous binder systems and combines high mechanical strength with problem-free application in electrostatic paint plants, for example high-rotation bells.